Pitch-halving integrated circuit process

ABSTRACT

A pitch-halving IC process is described. Parallel base line patterns are formed over a substrate, each being connected with a hammerhead pattern at a first or second side of the base line patterns, wherein the hammerhead patterns are arranged at the first side and the second side alternately, and the hammerhead patterns at the first or second side are arranged in a staggered manner. The above patterns are trimmed. A spacer is formed on the sidewalls of each base line pattern and the corresponding hammerhead pattern, including a pair of derivative line patterns, a loop pattern around the hammerhead pattern, and a turning pattern at the other end of the base line pattern. The base line patterns and the hammerhead patterns are removed. A portion of each loop pattern and at least a portion of each turning pattern are removed to disconnect each pair of derivative line patterns.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of and claims the prioritybenefit of U.S. application Ser. No. 13/845,038, filed on Mar. 17, 2013,now allowed. The entirety of the above-mentioned patent application ishereby incorporated by reference herein and made a part of thisspecification.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to integrated circuit (IC) fabrication, andparticularly to a pitch-halving IC process and an IC structure made bythe same process.

2. Description of Related Art

The resolution in a photolithography process depends on the wavelengthof the exposure light, the numerical aperture (NA) of the optical systemand the design of the photomask, and has a certain limit according tothe exposure conditions. When the resolution required by an array ofpatterns exceeds the resolution of the lithographic system, for example,in a case of forming the gate line array of a high-density memory like aDRAM of next generation, a pitch reduction method is needed, mainlybased on the spacer forming technique.

For example, patterns of dense conductive lines beyond lithographicresolution can be formed as follows. Parallel base line patterns arelithographically defined and trimmed, linear spacers having a smallerwidth/pitch and a double number are formed on the sidewalls of the baseline patterns, and then the base line patterns are removed, leaving thelinear spacers as the target line patterns beyond the lithographicresolution.

However, the contact pads of such small-pitch conductive lines aredifficult to form at the line ends, due to their larger width forsufficient electrical contact.

SUMMARY OF THE INVENTION

In view of the foregoing, this invention provides a pitch-halving ICprocess, which is particularly suitable for definition and formation ofdense conductive lines beyond the lithographic resolution and theircontact pads.

This invention also provides an IC structure that is made by thepitch-halving IC process of this invention.

The pitch-halving IC process of this invention is described as follows.A plurality of parallel base line patterns is formed over a substrate,each being connected with a hammerhead pattern at a first side or asecond side of the plurality of base line patterns, wherein thehammerhead patterns are arranged at the first side and the second sidealternately, and the hammerhead patterns at the first or second side arearranged in a staggered manner. Each base line pattern and eachhammerhead pattern are trimmed. A spacer is then formed on the sidewallsof each base line pattern and the corresponding hammerhead pattern,including a pair of derivative line patterns, a loop pattern around thehammerhead pattern, and a turning pattern at an end of the base linepattern without the corresponding hammerhead pattern. The base linepatterns and the hammerhead patterns are then removed. A portion of eachloop pattern and at least a portion of each turning pattern are removedto disconnect each pair of derivative line patterns, wherein theremaining loop pattern includes two contact pad patterns.

In an exemplary embodiment, the above process further includestransferring the patterns of the derivative line patterns and theremaining loop patterns to an underlying conductive layer. The patternedunderlying conductive layer includes: a plurality of conductive linescorresponding to the derivative line patterns, and a plurality ofcontact pads corresponding to the remaining loop patterns. In anotherexemplary embodiment, the derivative line patterns and the remainingloop patterns are directly conductive lines and their contact pads,respectively.

In addition, the pitch-halving IC process of this invention may furtherinclude forming a plurality of contact plugs over the contact pads.

The IC structure includes of this invention a plurality of parallelconductive lines and their contact pads. The conductive lines arearranged in a plurality of pairs. Each contact pad is connected with aconductive line at one end thereof, wherein the two contact pads of eachpair of conductive lines form an opened loop, the opened loops arearranged at a first side and a second side of the plurality ofconductive lines alternately, and the opened loops at the first orsecond side are arranged in a staggered manner.

The above IC structure may further comprise a plurality of contact plugsover the contact pads.

By arranging the hammerhead patterns at the same side of the base linepatterns in a staggered manner and utilizing the loop patterns formed asspacers around the hammerhead patterns to form the contact pad patterns,this invention allows the contact pads of the dense conductive lines tobe formed with a sufficient distance between each other as well as in ahigh die-area utilization efficiency.

In order to make the aforementioned and other objects, features andadvantages of this invention comprehensible, a preferred embodimentaccompanied with figures is described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2, 3 and 4 illustrate, in a top view, a pitch-halving ICprocess according to an embodiment of this invention, wherein FIG. 4also illustrates an IC structure according to the embodiment.

FIGS. 1A, 2A, 3A and 4A respectively illustrate, in a cross-sectionalview along the line A-A′, the structures illustrated in FIGS. 1, 2, 3and 4, respectively.

DESCRIPTION OF EMBODIMENTS

This invention is further explained with the following embodimentsreferring to the accompanying drawings, which are not intended to limitthe scope of this invention. For example, though the outer hammerheadpatterns at the first side and the second side of the plurality of baseline patterns have the same dimension as the inner ones in the directionperpendicular to the line, they can alternatively have a greaterdimension in the perpendicular direction, as long as a sufficientdistance can be provided between the two loop patterns formed around anytwo neighboring outer hammerhead patterns to make a sufficient distancebetween the two neighboring contact plugs that will be defined from thetwo loop patterns latter.

FIGS. 1, 2, 3 and 4 illustrate, in a top view, a pitch-halving ICprocess according to an embodiment of this invention, and FIGS. 1A, 2A,3A and 4A respectively illustrate, in a cross-sectional view along theline A-A′, the structures illustrated in FIGS. 1, 2, 3 and 4,respectively.

Referring to FIGS. 1 and 1A, a conductive layer 102, an etching masklayer 103, an anti-reflection coating (ARC) 104, and a patternedphotoresist layer 106 a+b of positive or negative type are formed over asubstrate 100 in sequence. The conductive layer 102 may include dopedpoly-Si, metal or a combination thereof. The etching mask layer 103 mayinclude a carbon layer. The substrate 100 as provided may have beenformed with other material layer. For example, in a case where theconductive layer 102 is to be defined into gate lines, the substrate hasbeen formed with a gate dielectric layer, such as a gate oxide layer ora high-k layer, before the conductive layer 102 is formed. The patternedphotoresist layer 106 a+b is defined by a lithography process.

The patterned photoresist layer includes a plurality of parallel baseline patterns 106 a, each of which is connected with a hammerheadpattern 106 b at a first side 12 or a second side 14 of the plurality ofbase line patterns 106 a. The hammerhead patterns 106 b are arranged atthe first side 12 and the second side 14 alternately, while thehammerhead patterns 106 b at the first side 12 or the second side 14 arearranged in a staggered manner. In addition, when the process of thisinvention is applied to form half-pitch conductive lines of ahigh-density memory array, there is an array area 10 on the substrate100, in which almost the entirety of each base line pattern 106 a islocated. The high-density memory array may be a high-density DRAM array.

It is noted that though the hammerhead patterns 106 b at the first side12 or the second side 14 as illustrated herein include only inner andouter sets of hammerhead patterns that are arranged in a 2-tieredmanner, this invention is not limited thereto. The hammerhead patterns106 b at each side may alternatively include multiple levels or multipletiers of staggered hammerhead patterns, such as 3 or 4 levels ofstaggered hammerhead patterns.

Though the base line patterns 106 a and the hammerhead patterns 106 binclude a photoresist material and are defined by a lithography processin the above case, the base line patterns and hammerhead patterns formedin this invention are not limited thereto. They may alternativelyinclude other material that can be trimmed narrowed, such as a suitablehard mask material, e.g., SiO_(x), Si₃N₄, carbon or poly-Si, etc. Insuch a case, the base line patterns and hammerhead patterns are definedby a patterned photoresist layer (not shown), and no anti-reflectioncoating is required under the unpatterned layer (not shown) from whichthe base line and hammerhead patterns are defined.

Referring to FIGS. 2 and 2A, each of the base line patterns 106 a andeach of the hammerhead patterns 106 b are trimmed to be narrower. Whenthe base line patterns 106 a and the hammerhead patterns 106 b include aphotoresist material, the trimming may utilize a dry etching process.

Thereafter, a spacer 110 a+b+c is formed on the sidewalls of eachtrimmed base line pattern 106 c and the corresponding trimmed hammerheadpattern 106 d, including a pair of derivative line patterns 110 a, aloop pattern 110 b around the trimmed hammerhead pattern 106 d, and aturning pattern 110 c at the end of the trimmed base line pattern 106 cwithout the corresponding trimmed hammerhead pattern 106 d. The spacersare usually formed by depositing a substantially conformal materiallayer on the trimmed (photoresist) patterns 106 c and 106 d and theexposed portions of the ARC 104 and then anisotropically etching thesame, such that only the portions of the material layer on the verticalsidewalls of the trimmed patterns 106 c and 106 d remain but theportions of the same on the horizontal surfaces are removed, wherein thematerial layer may include silicon oxide. The width of each spacer orderivative line pattern 110 a is controlled by the deposition thickness.The spacers may include low-temperature oxide (LTO) or ALD (atomic layerdeposition) oxide when the base line patterns 106 a and the hammerheadpatterns 106 b include a photoresist material. When the base linepatterns and the hammerhead patterns include a hard mask material, thespacers may include another material that can have a much lower removalrate than the hard mask material, such as SiO_(x), Si₃N₄, carbon orpoly-Si.

Referring to FIGS. 3 and 3A, all of the trimmed base line patterns 106 cand the trimmed hammerhead patterns 106 d are removed, possibly by usingO₂-plasma ashing or solvent stripping, leaving the derivative linepatterns 110 a, the loop patterns 110 b and the turning patterns 110 c(FIG. 2). For example, when the base line patterns 106 a and thehammerhead patterns 106 b include a photoresist material and the spacersinclude LTO, oxygen plasma can be used to remove the trimmed base linepatterns 106 c and the trimmed hammerhead patterns 106 d.

Thereafter, each turning pattern 110 c and a portion of each looppattern 110 b are removed to disconnect each pair of derivative linepatterns 110 a, such that each remaining loop pattern 110 d includes twocontact pad patterns. The removed portions of the loop patterns 110 band the removal of the turning patterns 110 c can be defined by chopopenings 120 a and 120 b, respectively. The chop openings 120 a and 120b are lithographically formed in a mask layer, such as a photoresistlayer.

In addition, though each turning pattern 110 c is entirely removed inthe above case, it is feasible to remove just a portion of each turningpattern 110 c as long as the connection between the corresponding pairof derivative line patterns 110 a is broken.

Referring to FIGS. 4 and 4A, after the patterned mask layer having thechop openings 120 a and 120 b therein is removed, the patterns of thederivative line patterns 110 a and the remaining loop patterns 110 d aretransferred to the underlying etching mask layer 103 and then to theunderlying conductive layer 102, basically by etching the etching masklayer 103 and the conductive layer 102 with the derivative line patterns110 a and the remaining loop patterns 110 d as a mask. The remainingetching mask layer 103 that serves as an etching mask during the finaletching stage is then removed or stripped away to leave only thepatterned conductive layer 102. The patterned conductive layer 102includes a plurality of conductive lines 102 a corresponding to thederivative line patterns 110 a, and a plurality of contact pads 102 bcorresponding to the remaining loop patterns 110 d. The conductive lines102 a may serve as a plurality of conductive lines of a memory array,such as the word lines of a memory array. The memory array may be a DRAMarray.

Then, a plurality of contact plugs 130 are formed over the contact pads102 b, wherein each contact plug 130 is formed over a contact pad 102 b.The contact plugs 130 may include a metal, such as tungsten (W).

Though the derivative line patterns 110 a and the remaining looppatterns 110 d are formed for defining an underlying conductive layer102 into half-pitch conductive lines and their contact pads in the abovecase, this invention is not limited thereto. It is also possible to omitan underlying conductive layer, choose a suitable material for the baseline and hammerhead patterns, and form a conductive spacer, such as ametal (e.g., TiN) spacer, on the sidewalls of each trimmed base linepattern and the corresponding trimmed hammerhead pattern, including apair of conductive derivative lines and a conductive loop pattern. Thus,after the trimmed base line patterns and the trimmed hammerheadpatterned are all removed and each conductive loop pattern is partiallyremoved through an aforementioned chop opening, the derivative lines andthe opened loop patterns can directly serve as conductive lines andtheir contact pads.

On other hand, when the original base line patterns 106 a have aline/space (L/S) width of F₁/F₁, each trimmed base line pattern 106 chas a feature size F₂, each derivative line pattern 110 a also has afeature size of F₂, and F₂=0.5 F₁, the derivative line patterns 110 ahave a constant pitch of 2 F₂ (=F₁). In an embodiment, F₁ is thelithography-limit feature size, F₂=0.5 F₁, the original base linepatterns 106 a have an L/S width of F₁/F₁ substantially, the trimmedbase line patterns 106 c have an L/S width of F₂/3 F₂ substantially, thederivative line patterns 110 a have an L/S width of F₂/F₂ substantially,so that a maximal density of the derivative line patterns 110 a with aconstant pitch of 2 F₂ are formed.

FIG. 4 also illustrates an IC structure according to the aboveembodiment of this invention. The structure includes a plurality ofparallel conductive lines 102 a arranged in a plurality of pairs, and aplurality of contact pads 102 b. Each contact pad 102 b is connectedwith a conductive line 102 a at one end of the conductive line 102 a,wherein the two contact pads 102 b of each pair of conductive lines 102a form an opened loop 102 c. The opened loops 102 c are arranged at afirst side 12 and a second side 14 of the plurality of conductive lines102 a alternately, and the opened loops 102 c at the first side 12 orthe second side 14 are arranged in a staggered manner.

The conductive lines 102 a may have an L/S width of 0.5 F/0.5 Fsubstantially, wherein F is the lithography-limited feature size. Suchconductive lines 102 a may serve as dense conductive lines of ahigh-density memory array, such as dense word lines of a high-densitymemory array. The memory array may be a DRAM array.

As described above, by arranging the hammerhead patterns at the sameside of the base line patterns in a staggered manner and utilizing theloop patterns formed as spacers around the hammerhead patterns to formthe contact pad patterns, this invention allows the contact pads of thedense conductive lines to be formed with a sufficient distance betweeneach other as well as in a high die-area utilization efficiency. Thisallows larger contacts to be defined while lowering the risk of shortingto an adjacent contact or corresponding landing pad. It is well knownthat defining larger contacts is easier than defining smaller contacts.

The method of this invention also allows for more overlay orregistration error between the contact layer and the underlying wordline layer, as explained above.

This invention has been disclosed above in the preferred embodiments,but is not limited to those. It is known to persons skilled in the artthat some modifications and innovations may be made without departingfrom the spirit and scope of this invention. Hence, the scope of thisinvention should be defined by the following claims.

What is claimed is:
 1. A pitch-halving integrated circuit (IC) process, comprising: forming, over a substrate, a plurality of parallel base line patterns each of which is connected with a hammerhead pattern at a first side or a second side of the plurality of base line patterns, wherein the hammerhead patterns are arranged at the first side and the second side alternately, and the hammerhead patterns at the first or second side are arranged in a staggered manner; trimming each base line pattern and each hammerhead pattern; forming, on sidewalls of each trimmed base line pattern and the corresponding trimmed hammerhead pattern as a spacer, a pair of derivative line patterns, a loop pattern around the trimmed hammerhead pattern, and a turning pattern at an end of the trimmed base line pattern without the corresponding trimmed hammerhead pattern; removing the trimmed base line patterns and the trimmed hammerhead patterns; and removing a portion of each loop pattern and at least a portion of each turning pattern to disconnect each pair of derivative line patterns, such that each remaining loop pattern includes two contact pad patterns.
 2. The pitch-halving IC process of claim 1, further comprising: transferring patterns of the derivative line patterns and the remaining loop patterns to an underlying conductive layer, wherein the patterned underlying conductive layer includes: a plurality of conductive lines corresponding to the derivative line patterns, and a plurality of contact pads corresponding to the remaining loop patterns.
 3. The pitch-halving IC process of claim 2, further comprising forming a plurality of contact plugs over the contact pads.
 4. The pitch-halving IC process of claim 1, wherein the derivative line patterns and the remaining loop patterns are directly a plurality of conductive lines and their contact pads, respectively.
 5. The pitch-halving IC process of claim 4, further comprising forming a plurality of contact plugs over the contact pads.
 6. The pitch-halving IC process of claim 1, wherein the base line patterns and the hammerhead patterns comprise a photoresist material.
 7. The pitch-halving IC process of claim 1, wherein the base line patterns as formed have a line/space (L/S) width of F₁/F₁ substantially, the trimmed base line patterns have an L/S width of F₂/3 F₂ (F₂=0.5 F₁) substantially, and the derivative line patterns have an L/S width of F₂/F₂ substantially.
 8. The pitch-halving IC process of claim 1, wherein the derivative line patterns are for defining a plurality of conductive lines of a memory array, or are directly a plurality of conductive lines of a memory array.
 9. The pitch-halving IC process of claim 8, wherein the memory array comprises a DRAM array.
 10. The pitch-halving IC process of claim 8, wherein the conductive lines are word lines of the memory array. 